Environmental compensation - HMP1 - HMP3 - HMP4 - HMP5 - HMP7 - HMP8 - HMP9 - HMPX - MMP8 - TMP1

HMP Series with MMP8 and TMP1 User Guide

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Environmental compensations improve the measurement accuracy of the probe. You can configure the settings with the Insight software or the Indigo80 handheld indicator, or using the Modbus protocol.

Pressure compensation

The pressure of the measured environment affects the accuracy of humidity calculations, especially calculations that are dependent on pressure (for example, mixing ratio). To achieve accurate output of all humidity parameters, you are recommended to update the value of the pressure compensation setpoint to match the environmental pressure when installing the probe.

For example, when you install the probe in a process with a pressure differing from normal atmospheric pressure, update the correct pressure into the pressure compensation setpoint parameter or register of the probe using the Insight software or the Indigo80 handheld indicator.

The current value is stored in non-volatile memory when the device is turned off, and restored at power-up.

Using the Modbus protocol, it is also possible to set the value to be read constantly from an external source, such as a pressure indicator.

Temperature compensation

You need to set an external source for the temperature compensation setpoint if the sensor warming feature of the condensation prevention function prevents the probe's own temperature measurement, and the output parameters that require temperature information to be known are required.

When warming is active, values of output parameters that depend on temperature measurement (for example, relative humidity) are unavailable, unless temperature information is read from an external source. Output parameters that can be measured or calculated without this external temperature information, such as dew point temperature, are available even without the temperature input.

The external temperature source can be another probe (for example, TMP1) that is connected to the same Indigo80 handheld indicator as your probe. It is also possible to use your own host system for updating the temperature value to your probe through the Modbus interface.

With a probe combination of TMP1 and HMP7 connected to the Indigo520 transmitter, TMP1 can function as the temperature source for HMP7. Other probe combinations are not supported directly, but you can still update the temperature value through the Modbus TCP/IP interface of Indigo520.

To get the most accurate measurement values, the external source needs to be able to provide the temperature compensation setpoint value constantly in real time, and the value needs to correspond to the temperature of the probe's measurement environment as accurately as possible. A suitable measurement point is as close to the probe as possible, but yet far enough so that ongoing condensation prevention warming of the probe does not have an effect on the measured value.

At device reset, the value is cleared.